(1) Field of the Invention
The present invention relates to an LCD panel, and more specifically to a PSA (polymer stabilized alignment) LCD panel.
(2) Description of the Prior Art
Due to rapid development in the display technology, an LCD (liquid crystal display) device is generally preferred to when compared to the conventional CRT-type display device due to its compact size and quick response time in addition to its lower power consumption and low radiation. Therefore, the LCD device is in great demand in the market and is widely used in many electronic devices, such as calculators, PDAs, notebook computers, digital cameras and mobile phones.
Due to market competition, the LCD manufacturers have devoted a tremendous effort in the research to improve the ability of the LCD device and simultaneously lower the cost. Therefore, the demand for the LCD device is increasing. Presently, the research is emphasized in the field how to widen the viewing angle of the LCD panel and shorten the response time for displaying the image.
In order to achieve the aforesaid objects, a MVA (multi-domain vertical alignment) design is implemented in the liquid crystal layer. During the construction of the LCD device, the common electrode and the pixel electrode are formed with protrusions or slits in order to control the splay of the crystal molecules when no voltage is applied on the liquid crystal layer, i.e. the crystal molecules are slightly inclined with respect to the protrusions. Thus, when the voltage is applied onto the pixel electrode, an electric field is generated that forces the crystal molecules in the liquid crystal layer to change their orientation from the slightly inclined direction to a predetermined direction, thereby shortening the response time so as to provide a wide viewing angle.
The multi-domain vertical alignment technology includes a film depositing process, an etching process and a photolithographic process to form the protrusion or slits on the common electrode and the pixel electrode. The production method is relatively complicated and results in the higher manufacturing cost. Moreover, since the protrusions formed on the substrate may hinder passage of light therethrough and the increased quantity thereof consequently reduces the number of the slits, which, in turn, lowers the brightness in the display panel of the LCD device.
The LCD manufacturers have introduced a PSA (polymer stabilized alignment) technology to solve the problems resulted by the use of the MVA (multi-domain vertical alignment) technology in the LCD device.
The LCD device generally includes a liquid crystal layer sandwiched between an upper substrate and a lower substrate. A common electrode is sandwiched between the liquid crystal layer and the upper substrate.
FIG. 1 shows a pixel structure of a conventional PSA LCD panel formed on a lower substrate, and includes a plurality of pixel units 10. Each pixel unit 10 includes a scan line 101, a data line 102, a thin film transistor 103, a storage capacitor 104, and a pixel electrode 105. During the operation, the scan line 101 is capable of transmitting a scan signal through the transistor 103 so as to permit transmission of the voltage signal from the data line 102 to the pixel electrode 105. At the same time, since the voltage signal fed through the data line 102 is retained within the storage capacitor 104, the pixel unit 10 can be kept under a preset gray value during the break of the data transmission.
As illustrated, the pixel electrode 105 includes a pattern having a plurality of parallel ribs extending along four directions (the pattern has a fish-bone configuration). Under the operation, an electric field is resulted between the pixel electrode 105 and the common electrode so as to force the crystal molecules to change their orientation. The crystal molecules change their orientation towards the four directions due to the configuration of the pixel electrode 105 so as to form four domains with respect to the center thereof.
In order to shorten the response time for displaying the image, after the pixel electrode 105 being constructed as the aforesaid manner, the PSA (polymer stabilized alignment) technology is implemented onto the pixel electrode 105 so as to direct the crystal molecules within the liquid crystal layer in a predetermined inclined angle. In other words, during construction of the aforesaid PSA LCD panel, the monomers are added into the liquid crystal layer such that when the voltage signal is applied onto the common electrode and the pixel electrode 105, the crystal molecules tend in the predetermined inclined angle with the monomers tending the same direction. A power light (visible or ultra violet light) or heat treatment is conducted such that the monomers combined together to form the polymers tending in the predetermined inclined angle.
When no voltage is applied, the crystal molecules tend in the predetermined inclined angle under the influence of the polymers. When driven by an electric field, the crystal molecules can turn swiftly from the predetermined inclined angle into the appropriate position, thereby shortening the response time for displaying the image.
Moreover, since the PSA LCD panel is not provided with the protrusions or slits, it is free from light leakage problem when compared to the MVA LCD panel. Thus, the PSA LCD panel has a high contrast and a higher brightness than the MVA LCD panel.
Presently, the pixel electrode 105 in the PSA LCD panel is made from ITO (indium tin oxide). Lithographic and etching processes are conducted to form the pattern with a fish-bone configuration having a plurality of parallel ribs divided in four domains with respect to a center, which, in turn, provides a higher contrast, a higher brightness and a shorter response time. However, it is in the trend to produce the LCD panel in a larger dimension, the aforesaid design is unable to solve the color-shift in the changing view angle and reduce the color washout phenomenon.